FIG. 1 is an illustration of selected components of a disk drive 10 according to the prior art. The disk drive includes at least one magnetic recording disk 12 that rotates on spindle 13 in direction 15 driven by a spindle motor (not shown). Housing or baseplate 16 provides support for the components. The upper portion of the outer protective case, which is present for normal operation, is removed for this illustration. The data is recorded in concentric or spiral data tracks 26 that are generally circular. Only a small sample of the many tracks are shown. In practice there are thousands of tracks that extend 360 degrees around the disk. The disk drive includes actuator 14 that pivots on pivot point 17 driven by a rotary voice coil motor (VCM) (not shown). The actuator 14 includes a rigid actuator arm 18. A flexible wiring cable 24, which is usually called the “flex cable,” connects the devices on the actuator including read and write heads (not shown) in the slider 22 and the read/write integrated circuit chip (R/W IC) 21 shown) to the drive's electronics (not shown). The R/W IC 21, which is also variously called the arm electronics IC, preamplifier chip or preamp, is typically mounted on the actuator arm or integrated into the flex cable. A suspension 20, which is attached to the end of arm 18, includes a flexure/gimbal element (not shown) on which the air-bearing slider 22 is mounted to allow flexible movement during operation. As the disk 12 rotates, the slider with read/write heads is positioned over a track to read and write the magnetic transitions. Disk drives often have more than one disk mounted on the spindle and the upper and lower surfaces of each disk can have magnetic recording material thereon, and the actuators with components mounted thereon are replicated as needed to access each of the recording surfaces.
The flex cable 24 provides electrical connections between the actuators and the drive electronics on a circuit board (not shown). The flex cable 24 is rigidly attached by stationary bracket 23 at one end, which connects to drive electronics. The other end of the flex cable is attached to the set of actuators 14 which move in unison in response to the VCM.
A plurality of electrical paths (not shown) extend from the flex cable along the actuators to the arm electronics chip 21. The arm electronics chip is in turn connected by a plurality of electrical paths that extend through the suspension 20 and connect to the slider 22 as further illustrated in FIG. 2. These electrical paths are typically called traces 31 and are made of copper. The load beam structure of the suspension is a spring metal layer. The tail end of the suspension has a set of tail termination pads 33 for electrical connection to the corresponding traces 31. The traces carry the signals for the reader (read head), writer (write head) in the slider, as well as any additional signals required for fly height control, heater, etc. The example suspension in FIG. 2 has 8 termination pads that provide connection to 8 slider connection pads 35 that are in turn connected to the slider (not shown) at the slider (or head) end 20H of the suspension. Higher or lower numbers of pads and corresponding traces can be used. The traces can vary in width and additional structures/features can be included in the paths to control electrical parameters such as impedance. Dielectric material separates the traces from the spring metal layer and a covering layer dielectric material is typically deposited over the traces. Subtractive and/or additive photolithography, deposition and etching processes can be used to manufacture suspensions and form the traces.
Typically the spring metal layer in the suspension has been used as a ground plane for the traces. Because of the spatial constraints imposed on the suspension a multi-layer or stacked trace configurations have been used. Klaassen et al. in U.S. Pat. No. 6,608,736 disclose stacked read line traces arranged on top of each other and separated from each other by a dielectric layer and separated from the stainless steel base layer by another dielectric layer.
In U.S. Pat. No. 7,701,674 to Hajime Arai (Apr. 20, 2010) a suspension with an enhanced high conductivity ground layer trace under the write traces is described, which lowers the write trace impedance and lower signal transmission loss. The high conductivity ground layer is formed by plating copper directly onto the stainless steel substrate prior to the formation of the write traces and is, therefore, not electrically separated from the stainless steel. The high conductivity ground layer can be a single or double trace. Arai notes that the high conductivity ground layer may be extended to the area of the heater wires unless the impedance of the read wires is thereby decreased.
U.S. Pat. No. 8,094,413 to Hentges, et al. Jan. 10, 2012 describes a disk drive head/slider suspension flexure with stacked traces having differing configurations on the gimbal and beam regions. A head suspension is described that includes integrated lead suspension flexure having stacked traces that run along one side of the spring metal layer and multi-layer traces that run along the other side. The traces come together in the tail region of the suspension where the set termination pads provide electrical connection to the system. The head suspension component includes stacked traces having first and second traces in the first and second conductor layers, respectively. The stacked traces are used for the writer in an embodiment and the multilayer traces are used for the reader and fly height traces and include a ground layer.
U.S. Pat. No. 8,233,240 to Contreras, et al. Jul. 31, 2012 describes an integrated lead suspension (ILS) in a magnetic recording disk drive has the transmission line portion of the ILS between the flex cable termination pads at the tail and the gimbal area formed of multiple interconnected segments, each with its own characteristic impedance. At the interface between any two segments there is a change in the widths and in impedance of the electrically conductive traces of the transmission line. The number of segments and their characteristic impedance values are selected to produce the largest frequency bandwidth with a substantially flat phase delay from the write driver to the write head.
U.S. Pat. No. 6,088,235 issued to Chiao, et al. Jul. 11, 2000 describes a method of magnetic interference (noise) cancellation in a single-ended MR preamplifier front end using a balanced ground return path in a flex circuit connecting an MR head to the front end of the preamplifier. The pattern of conductive traces includes a signal path extending from a trace pad aligned with the preamplifier signal input pin to a distal signal input connection pad for connecting to a head and a plurality of ground return paths leading from a vicinity of the distal signal input connection pad to the at least two ground pins. The plurality of ground return paths are so arranged that a common mode interference induces currents in opposite directions in the ground return paths. The interference currents are therefore combined and canceled at a preamplifier connected to the preamplifier signal input pin within the integrated circuit. The balanced ground return path introduces a interference current in the opposite direction of the original interference current as viewed at the signal input pins of the preamplifier chip. In this manner common mode rejection of the radiated interference component is restored in the single-ended MR preamplifier circuit arrangement.
Although stainless steel has advantages a structural material for suspensions, conductive traces for the read signal from the read head in a slider are highly susceptible to interference signal coupling onto the read signal path and degrading the SNR signals performance. Systems that include sliders with multiple read heads for two dimensional magnetic recording (TDMR) are expected to use single-ended preamplifiers and to be more sensitive to extrinsic interference signals. Two main sources of interference onto the stainless steel suspensions are 1) crosstalk from the write signal; and 2) radio frequency interference (RFI) that leaks into a disk drive's enclosure from external sources. In current designs all traces (sensitive reader traces, as well as, interference-signal insensitive traces), share the same signal return path to ground though the stainless steel layer.